Image processing apparatus and method for setting wide dynamic range mode based on luminance of image

ABSTRACT

Provided is an image processing apparatus which generates a wide dynamic range (WDR) image using an image sensor. The image processing apparatus includes: an image sensor which outputs image data having a plurality of image channels; a mode setting unit which changes a photographing mode from a first mode in which a first number of sub-images are synthesized to a second mode in which a second number of sub-images are synthesized, based on luminance of the output image data; a register setting unit which changes a register value of the image sensor according to the second mode; and an image signal processor (ISP) which generates a result image by synthesizing the second number of sub-images from the image data according to the changed register value, wherein the second number of sub-images have different exposure times.

CROSS-REFERENCE TO THE RELATED APPLICATION

This application claims priority from Korean Patent Application No.10-2016-0128866, filed on Oct. 6, 2016, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference in its entirety.

BACKGROUND 1. Field

Methods and apparatuses consistent with exemplary embodiments relate toan image processing apparatus, and more particularly, to an apparatusand method for generating a wide dynamic range (WDR) image using animage sensor.

2. Description of the Related Art

A solid-state pickup device such as a charge-coupled device (CCD) imagesensor or a complementary metal oxide semiconductor (CMOS) image sensorused in a video camera or a digital camera performs photoelectricconversion. That is, such a device accumulates electric charge accordingto the amount of incident light and outputs an electrical signalcorresponding to the accumulated charge. However, there is an upperlimit to the amount of electric charge accumulated by a photoelectricconverter. In addition, when more than a certain amount of light isreceived, the amount of accumulated charge reaches a saturation level,resulting in the so-called ‘white noise’ that causes a subject area withmore than a certain level of brightness to have a saturated luminancelevel.

To prevent this phenomenon, a high shutter speed may be used for abright subject to reduce an exposure time. The reduced exposure time mayreduce the charge accumulation period of the photoelectric converter.Therefore, an electrical signal may be output before the amount ofaccumulated charge reaches the saturation level. Such processing makesit possible to output an image which accurately reproduces gray levelsof the subject. However, if a subject having a mixture of bright anddark parts is taken with a high shutter speed, an exposure time may notbe sufficient for the dark part. As a result, a signal-to-noise ratio(SNR) may be reduced, thereby deteriorating image quality.

To accurately reproduce luminance levels of a bright part and a darkpart of a subject, it is required to achieve a high SNR by applying along exposure time to pixels with a small amount of incident light whileapplying additional processing to pixels with a large amount of incidentlight to avoid the saturation.

To this end, a plurality of images may be taken successively withdifferent exposure times and then synthesized together. Specifically, along-exposed image and a short-exposed image may be taken successivelyand individually. Then, the long-exposed image is used for a dark partand the short-exposed image is used for a bright part in whichwhitening-out occurs in the long exposed image. This technology iscalled ‘wide dynamic range (WDR)’ technology.

A WDR image may be generated by synthesizing a plurality of images withdifferent exposure times using the WDR technology. For example, a morenatural image can be obtained using the WDR technology in variousphotographing environments such as taking a photograph in a placeagainst the sun (e.g., near the window), taking a photograph of a scenewith a mixture of bright and dark parts (e.g., a night view), and takinga photograph of a scene with a mixture of a bright part in the sun and adark part in the shade (e.g., a sports event).

FIG. 1 illustrates an example of conventional WDR image generationtechnology. Referring to FIG. 1, an image sensor which supports up to120 frames per second (fps) of shutter speed generates one WDR frame bysynthesizing four sub-images. Although each of the four sub-images couldbe taken using 120 fps shutter speed, only up to 30 fps is allowed toeach of the four sub-images because the sub-images are to be synthesizedinto one WDR frame. For example, the four sub-images may be taken withdifferent shutter speeds (i.e., exposure times) of very long (VL), long(L), short (S), and very short (VS), respectively. Due to the differentshutter speeds, the four sub-images have different luminance.

Thus, the WDR synthesis technology cannot fully utilize a maximumshutter speed. That is, in a 4WDR mode of FIG. 1, the exposure time ofthe image sensor is only about a quarter of the exposure time in anormal mode in which WDR is not used. In other words, the amount oflight provided to the image sensor is reduced to ¼ compared to thenormal mode. This shortage of light significantly reduces image qualityof a final image if WDR is applied in a dark environment. In particular,the shortage of light increases a sensor gain, thereby sharplyincreasing noise.

SUMMARY

Aspects of the inventive concept provide an image processing apparatusand method which can prevent deterioration of image quality through arapid change between various wide dynamic range (WDR) modes including anormal mode (no WDR synthesis mode) according to an environment in whichan image is captured.

Aspects of the inventive concept also provide an image processingapparatus and method which support a seamless WDR mode change byminimizing a delay in the automatic WDR mode change.

However, aspects of the inventive concept are not restricted to the oneset forth herein. The above and other aspects of the inventive conceptwill become more apparent to one of ordinary skill in the art to whichthe inventive concept pertains by referencing the detailed descriptionof the inventive concept given below.

According to an aspect of an exemplary embodiment, there is provided animage processing apparatus including: an image sensor configured tooutput image data having a plurality of image channels; at least oneprocessor to implement: mode setting unit configured to change aphotographing mode from a first mode in which a first number ofsub-images are synthesized to a second mode in which a second number ofsub-images are synthesized, based on luminance of the output image data;a register setting unit configured to change a register value of theimage sensor according to the second mode; and an image signal processor(ISP) configured to generate a result image by synthesizing the secondnumber of sub-images from the image data according to the changedregister value, wherein the second number of sub-images have differentexposure times.

The register value may include a maximum shutter speed for eachphotographing mode and a shutter speed for each image channel.

The maximum shutter speed may be set in inverse proportion to a numberof sub-images to be synthesized for generating the result image.

The number of image channels output from the image sensor may beconstant regardless of the photographing mode.

The ISP may read the second number of image channels according to thesecond mode among the image channels included in the image data outputfrom the image sensor and generates the result image by synthesizing thesecond number of sub-images.

The ISP may include: a channel writer configured to sequentially recordin an input channel buffer the image channels included in the image dataoutput from the image sensor according to the second mode; a channelreader configured to read the second number of image channels among theimage channels recorded in the input channel buffer and record thesecond number of image channels in an output channel buffer; and a widedynamic range (WDR) image generator configured to synthesize sub-imagescorresponding to the second number of image channels recorded in theoutput channel buffer.

The WDR image generator may include: a sub-image generation unitconfigured to generate the second number of sub-images respectively fromthe second number of image channels recorded in the output channelbuffer; and an image synthesis unit configured to generate the resultimage by synthesizing the second number of sub-images.

The image synthesis unit may generate the result image by assigning adifferent weight to each of the second number of sub-images or to eacharea of each of the second number of sub-images.

Each of the first number and the second number may be an integer equalto or greater than 1.

Each of the first number and the second number may be a power of 2.

The first number is 4, and the second number may be 2 or 1.

The mode setting unit may determine the luminance of the output imagedata based on a mean of luminance of pixels included in the output imagedata.

The mode setting unit may determine the luminance of the output imagedata based on a proportion of dark pixels whose luminance is equal to orlower than a first predetermined level in the output image data or theproportion of bright pixels whose luminance is equal to or higher than asecond predetermined level in the output image data.

According to another aspect of an exemplary embodiment, there isprovided an image processing method including: outputting image datahaving a plurality of image channels using an image sensor; changing aphotographing mode from a first mode in which a first number ofsub-images are synthesized to a second mode in which a second number ofsub-images are synthesized, based on luminance of the output image data;changing a register value of the image sensor according to the secondmode; outputting modified image data corresponding to the changedregister value; and generating a result image by synthesizing the secondnumber of sub-images from the modified image data, wherein the secondnumber of sub-images have different exposure times.

The register value may include a maximum shutter speed for eachphotographing mode and a shutter speed for each image channel.

The maximum shutter speed may be set in inverse proportion to a numberof sub-images to be synthesized for generating the result image.

The number of image channels output from the image sensor may beconstant regardless of the photographing mode.

The generating of the result image may include reading the second numberof image channels according to the second mode among the image channelsincluded in the modified image data and generating the result image bysynthesizing the second number of sub-images.

The generating of the image may include: sequentially recording theimage channels included in the modified image data in an input channelbuffer; reading the second number of image channels among the imagechannels recorded in the input channel buffer; recording the secondnumber of image channels in an output channel buffer; and synthesizingsub-images corresponding to the second number of image channels recordedin the output channel buffer.

The synthesizing of the second number of sub-images may include:generating the second number of sub-images respectively from the secondnumber of image channels recorded in the output channel buffer; andgenerating the result image by synthesizing the second number ofsub-images.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the embodiments, taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates a conventional wide dynamic range (WDR) imagegeneration technology;

FIG. 2 is a block diagram of an image processing apparatus according toan exemplary embodiment;

FIG. 3 illustrates a process of switching from a 4WDR mode to a 2WDRmode by resetting a WDR image sensor and an image signal processor(ISP), according to an exemplary embodiment;

FIG. 4 illustrates a process of switching from a 4WDR mode to a 2WDRmode by changing a register value of a WDR image sensor according to anexemplary embodiment;

FIG. 5 illustrates a process of switching from a 4WDR mode to a normalmode by changing a register value of a WDR image sensor according to anexemplary embodiment;

FIG. 6 is a detailed block diagram of an ISP according to an exemplaryembodiment;

FIG. 7 illustrates an ISP operating in a 4WDR mode, according to anexemplary embodiment;

FIG. 8 illustrates an ISP operating in a 2WDR mode, according to anexemplary embodiment;

FIG. 9 illustrates an ISP operating in a normal mode, according to anexemplary embodiment;

FIG. 10 is a block diagram of a WDR image generator according to anexemplary embodiment;

FIG. 11 illustrates a process of synthesizing sub-images using an imagesynthesis unit according to an exemplary embodiment; and

FIG. 12 is a flowchart illustrating an image processing method accordingto an exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

Advantages and features of the inventive concept and methods ofaccomplishing the same may be understood more readily by reference tothe following detailed description of preferred exemplary embodimentsand the accompanying drawings. The inventive concept may, however, beembodied in many different forms and should not be construed as beinglimited to the exemplary embodiments set forth herein. Rather, theseexemplary embodiments are provided so that this disclosure will bethorough and complete and will fully convey the inventive concept tothose skilled in the art, and the present inventive concept will only bedefined by the appended claims. Throughout the specification, likereference numerals in the drawings denote like elements. Hereinafter,exemplary embodiments will be described in detail with reference to theaccompanying drawings.

FIG. 2 is a block diagram of an image processing apparatus 100 accordingto an exemplary embodiment.

Referring to FIG. 2, light reflecting from a subject is guided to a widedynamic range (WDR) image sensor 30 by a photographing lens 20 andconverted into image data (an electrical signal) by the WDR image sensor30. The WDR image sensor 30 may support a WDR function. That is, the WDRimage sensor 30 may provide a plurality of sub-images (e.g., foursub-images as in FIG. 1) corresponding to a plurality of image channels(image output channels). The sub-images are image data obtained underdifferent photographing conditions and used as source images to generateone WDR image.

A WDR mode setting unit 60 may calculate luminance of the image dataoutput from the WDR image sensor 30 and set an appropriate WDR modebased on the calculated luminance. That is, the WDR mode setting unit 60may change modes from a first mode in which a first number of sub-imagesare synthesized to a second mode in which a second number of sub-imagesare synthesized based on the calculated luminance. For example, when acurrent mode is a normal mode in which one sub-image is generated (thatis, WDR synthesis is bypassed because the number of sub-images is one),the WDR mode setting unit 60 may change the current mode to a 2WDR mode,in which two sub-images are synthesized, based on the calculatedluminance. Specifically, when the current mode is a 4WDR mode in whichfour sub-images are synthesized, if the luminance is lower than a firstreference value due to insufficient light input to the photographinglens 20, the current mode may be changed to the 2WDR mode in which twosub-images are synthesized. However, if the luminance is still too lowin the 2WDR mode (e.g., if the luminance is even lower than a secondreference value that is below the first reference value), the currentmode may be changed to the normal mode in which WDR synthesis isdisabled.

The luminance used as a criterion for changing modes may be the mean ofluminance of pixels included in the output image data. Alternatively,the luminance of the output image data may be defined based on a ratioof the number of dark pixels whose luminance is equal to or lower than apredetermined level to the total number of pixels included in the outputimage data or based on a ratio of the number of bright pixels whoseluminance is equal to or higher than a predetermined level to the totalnumber of pixels included in the output image data. The luminance canalso be defined in other ways as long as it can represent the luminanceof the output image data.

When the WDR mode setting unit 60 determines to change the current WDRmode to a new WDR mode, the image processing apparatus 100 may start thenew WDR mode by resetting not only the WDR image sensor 30 but also animage signal processor (ISP) 70.

Various modules (i.e., units, controllers, processors, etc.) of theimage processing apparatus 100 shown in FIG. 2 may be implemented withone or more processors.

FIG. 3 illustrates a process of switching from the 4WDR mode to the 2WDRmode by resetting the WDR image sensor 30 and the ISP 70.

Referring to FIG. 3, since the current mode is the 4WDR mode, foursub-images A, B, C and D obtained under different photographingconditions form one WDR unit N−1. Here, a WDR unit refers to one WDRimage obtained from a plurality of sub-images, and N−1, N or N+1indicates a time sequence of the WDR unit. When the WDR mode settingunit 60 determines to change the current mode to the 2WDR mode asindicated by reference numeral 90, both the WDR image sensor 30 and theISP 70 are reset. After the current mode is changed to the 2WDR mode,two sub-images A and B or C and D form one WDR unit N and/or N+1.

To change WDR modes in this way, the ISP 70 should be reset as describedabove, and normally it takes a considerable time (approximately 2 to 3seconds) to reset the ISP 70. Since no image is generated during thattime, an output video may be temporarily frozen. This cannot only causeinconvenience to a user but also lead to a reduction in the performanceand quality of the apparatus 100.

Therefore, exemplary embodiments in which WDR modes can be changedrapidly without the need to wait until the ISP 70 is reset willhereinafter be described.

In FIG. 2, when the WDR mode setting unit 60 determines to change thecurrent mode to another mode (i.e., the second mode), a sensorcontroller 42 changes a register value of the WDR image sensor 30according to the second mode. Here, the register value is a parameterused by the sensor controller 42 to control various photographingconditions of the WDR image sensor 30. Preferably, the register valuemay include a maximum shutter speed Vmax and a shutter speed set foreach image channel. The maximum shutter speed Vmax is a maximum exposuretime that can be secured by one image channel, and the shutter speed setfor each image channel is a shutter speed (very long (VL), long (L),short (S), very short (VS), etc.) actually allocated to each imagechannel. There is virtually no time delay in changing the register valueof the WDR image sensor 30, compared to resetting the ISP 70 as in FIG.3.

FIG. 4 illustrates a process of switching from the 4WDR mode to the 2WDRmode by changing the register value of the WDR image sensor 30.

Referring to FIG. 4, since the current mode is the 4WDR mode, foursub-images A, B, C and D obtained under different photographingconditions form one WDR unit N−1. When the WDR mode setting unit 60determines to change the current mode to the 2WDR mode as indicated byreference numeral 90, a register setting unit 50 changes the registervalue of the WDR image sensor 30. The register values may include themaximum shutter speed Vmax and the shutter speed set for each imagechannel. In this example, the maximum shutter speed Vmax may be set totwice a current maximum shutter speed Fs of each image channel, and twoshutter speeds are alternately allocated to the image channels. Theregister setting unit 50 may control the accumulation time of anelectronic shutter by controlling the reset timing of the WDR imagesensor 30 and change the register value accordingly.

Therefore, in FIG. 4, the shutter speeds of the image channels A, B, Cand D may be set to L, S, L, and S, respectively. However, since the ISP70 has not been reset for a mode change, the number of image channelsoutput from the WDR image sensor 30, i.e., the number of image channelsincluded in a WDR unit N, is still four. If the ISP 70 is reset as inFIG. 3, the number of image channels included in a WDR unit is reducedto two.

In FIG. 4, after the register setting unit 50 changes the registervalue, the current mode can be changed to the 2WDR mode virtuallywithout a delay. That is, one 2WDR image frame can be obtained bysynthesizing the first two A and B of the four image channels A, B, Cand D, and another 2WDR image frame can be obtained by synthesizing theother two image channels C and D. Therefore, while two WDR units N−1 andN are illustrated in FIG. 4, the number of WDR image frames obtainedfrom the two WDR units N−1 and N is three as in FIG. 3.

FIG. 5 illustrates a process of switching from the 4WDR mode to thenormal mode by changing the register value of the WDR image sensor 30.

Referring to FIG. 5, since the current mode is the 4WDR mode, foursub-images A, B, C and D obtained under different photographingconditions form one WDR unit N−1. When the WDR mode setting unit 60determines to change the current mode to the normal mode (no WDR mode or1WDR mode) as indicated by reference numeral 90, the register settingunit 50 sets the maximum shutter speed Vmax of the WDR image sensor 30to four times the current maximum shutter speed Fs of each image channeland allocates the same shutter speed to the four image channels.Therefore, the shutter speeds of the image channels A, B, C and D mayall be set to L. Even in this case, the number of image channels outputfrom the WDR image sensor 30, i.e., the number of image channelsincluded in a WDR unit N, is still four.

After the register setting unit 50 changes the register value, thecurrent mode can be changed to the normal mode virtually without adelay. That is, four image frames (normal frames) can be obtainedrespectively from the four image channels A, B, C and D set to the sameexposure time (L) without a synthesizing process. Therefore, while twoWDR units N−1 and N are illustrated in FIG. 5, the number of imageframes obtained from the two WDR units N−1 and N is five.

After the register value of the WDR image sensor 30 is changed accordingto a mode change by the WDR mode setting unit 60, the WDR image sensor30 outputs modified image data having the same number of image channelsas before but having the changed parameter (e.g., shutter speed), asillustrated in FIGS. 4 and 5. Here, the maximum shutter speed Vmax maybe set in inverse proportion to the number of sub-images correspondingto a new WDR mode. For example, in FIG. 4, the maximum shutter speedVmax is set to twice the current maximum shutter speed Fs according to amode change from the 4WDR mode to the 2WDR mode. In FIG. 5, the maximumshutter speed Vmax is set to four times the current maximum shutterspeed Fs according to a mode change from the 4WDR mode to the normalmode.

To completely change WDR modes, it is required to change the operationof the ISP 70 as well as the register value of the WDR image sensor 30.This is because the ISP 70 has to generate a WDR image by synthesizingthe changed number (i.e., the second number) of sub-images from themodified image data. In the example of FIG. 5, the ISP 70 may read aplurality of image channels A, B, C and D included in the image dataoutput from the WDR image sensor 30. Unless the ISP 70 is reset, the ISP70 may use the four sub-images instead of two of them to generate oneWDR image, even after the photographing mode, i.e., WDR mode, haschanged to a new mode, i.e., 4WDR mode.

FIG. 6 is a detailed block diagram of the ISP 70 according to anexemplary embodiment. The ISP 70 may include a channel writer 72, aninput channel buffer 74, a channel reader 76, an output channel buffer78, and a WDR image generator 80. The input channel buffer 74 and theoutput channel buffer 78 can be provided outside the ISP 70. Each of theinput channel buffer 74 and the output channel buffer 78 may beimplemented as a storage medium for temporarily storing data, such as arandom access memory (RAM), a flash memory, a solid state disk (SSD),etc.

The channel writer 72 sequentially records a plurality of image channelsincluded in image data output from the WDR image sensor 30 according toa current mode in the input channel buffer 74. The channel reader 76reads the image channels recorded in the input channel buffer 74 inunits of the second number of image channels according to mode changeinformation. The mode change information may indicate that the WDR modehas changed to the second mode, and may be provided by the WDR modesetting unit 60. Further, the channel reader 76 record the read imagechannels in the output channel buffer 78. Then, the WDR image generator80 synthesizes sub-images corresponding to the second number of imagechannels recorded in the output channel buffer 78 and outputs thesynthesis result to outside the ISP 70.

FIGS. 7 through 9 respectively illustrate, in more detail, the operationof the ISP 70 in the 4WDR mode, the 2WDR mode, and the normal mode.Referring to FIG. 7, in the 4WDR mode, the WDR image sensor 30 outputsimage data having different shutter speeds (VL, L, S, and VS) for fourimage channels A, B, C and D in response to a voltage VD applied to theWDR image sensor 30. Here, a direct memory access (DMA) writer 72 (orthe channel writer) sequentially records the image channels A, B, C andD included in the image data according to the current mode in the inputchannel buffer 74. A DMA reader 76 (or the channel reader) reads each ofthe four image channels A, B, C and D and stores the read four imagechannels A, B, C and D, as they are, in the output channel buffer 78.Accordingly, the WDR image generator 80 generates one WDR image bysynthesizing four sub-images corresponding to the four image channels A,B, C and D stored in the output channel buffer 78. Here, the arrangementof the channels A, B, C and D stored in the input channel buffer 74 andthe arrangement of the channels A, B, C and D stored in the outputchannel buffer 78 are the same, and a frame number n of the final WDRimage is constant.

Referring to FIG. 8, in the 2WDR mode, the WDR image sensor 30 outputsimage data having two shutter speeds (L, S, L and S) alternatelyallocated to four image channels A, B, C and D in response to thevoltage VD applied to the WDR image sensor 30. Here, a period of timeduring which the voltage VD applied to the WDR image sensor 30 ismaintained. That is, the maximum shutter speed Vmax is set to twice thecurrent maximum shutter speed Fs (i.e., Fs×2) in the 4WDR mode by theregister setting unit 50.

The DMA writer 72 sequentially records the image channels A, B, C and Dincluded the image data output by the image sensor 20, according to thecurrent mode in the input channel buffer 74. The DMA reader 76 readseach of the four image channels A, B, C and D and stores the read fourimage channels A, B, C and D in the output channel buffer 78 in units oftwo channels. Accordingly, the WDR image generator 80 generates ann^(th) WDR image by synthesizing two sub-images corresponding to twoimage channels A and B stored in the output channel buffer 78. Inaddition, the WDR image generator 80 generates an (n+1)^(th) WDR imageby synthesizing two sub-images corresponding to the remaining two imagechannels C and D stored in the output channel buffer 78.

Referring to FIG. 9, in the normal mode, the WDR image sensor 30 outputsimage data having the same shutter speed (L) for four image channels A,B, C and D in response to the voltage VD applied to the WDR image sensor30. Here, the period of time during which the voltage VD applied to theWDR image sensor 30 is maintained. That is, the maximum shutter speedVmax is set to four times the current maximum shutter speed Fs (Fs×4) inthe 4WDR mode by the register setting unit 50.

The DMA writer 72 sequentially records the image channels A, B, C and Dincluded the image data according to the current mode in the inputchannel buffer 74. The DMA reader 76 reads each of the four imagechannels A, B, C and D and stores the read four image channels A, B, Cand D in the output channel buffer 78 in units of one channel.Accordingly, the WDR image generator 80 generates an n^(th) normal imagefrom one image channel A stored in the output channel buffer 78.Similarly, the WDR image generator 80 generates an (n+1)^(th) normalimage, an (n+2)^(th) normal image and an (n+3)^(th) normal image fromthe image channel B, the image channel C and the image channel D,respectively.

FIG. 10 is a detailed block diagram of the WDR image generator 80according to an exemplary embodiment. The WDR image generator 80 mayinclude a channel input unit 82, sub-image generation units 84 a through84 k, an image synthesis unit 86, and an image post-processing unit 88.

The channel input unit 82 sequentially receives the second number ofimage channels recorded in the output channel buffer 78 according to thesecond mode. The sub-image generation units 84 a through 84 k generatethe second number of sub-images from the second number of image channelssequentially input to the channel input unit 82. The image synthesisunit 86 generates a WDR image by synthesizing pixels of the secondnumber of sub-images. Here, the pixels may have, but not limited to, anRGB data format, a YUV data format, or an YCbCr data format. Inaddition, the image post-processing unit 88 post-processes the WDR imagegenerated by the image synthesis unit 86. The post-processing mayinclude, but is not limited to, white balance adjustment, gammaprocessing, gain adjustment, etc.

FIG. 11 illustrates a process of synthesizing sub-images using the imagesynthesis unit 86.

Referring to FIG. 11, the first sub-image generation unit 84 a generatesa first sub-image taken with a relatively long exposure time, i.e., slowshutter speed, and the second sub-image generation unit 84 b generates asecond sub-image 94 taken with a relatively short exposure time, i.e.,fast shutter speed.

The image synthesis unit 86 obtains a first weighted sub-image 96 byapplying a first weight to the first sub-image 92 and obtains a secondweighted sub-image 98 by applying a second weight to the secondsub-image 94. Then, the image synthesis unit 86 generates one WDR image95 by adding corresponding pixels in the first and second weightedsub-images 96 and 98. Here, the sum of the first weight and the secondweight may be 1. A weight may be given to each sub-image or to each area(or block) of a sub-image. In FIG. 11, two sub-images are synthesized.However, two or other numbers of sub-images can be synthesized in thesame way as described above.

Referring back to FIG. 2, a WDR image (a still image or a moving image)generated by the ISP 70 may be stored in an image memory 26. An imagedisplay unit 28 may be a liquid crystal display (LCD), an organiclight-emitting diode (OLED), a cathode ray tube (CRT), etc. and displaythe WDR image recorded in the image memory 26 on the screen. Inaddition, the image display unit 28 may be turned on or off by amanipulation unit 43.

An image encoding unit 41 may read the WDR image stored in the imagememory 26, compress the read WDR image, and store the compressed WDRimage again in the image memory 26.

The manipulation unit 43 is a unit used to input various instructions ofa system processor 40. The manipulation unit 43 may be implemented inthe form of a switch, a dial, a touch panel, a pointing device based oneye detection, a voice recognition device, or a combination of the same.Using the manipulation unit 43, a user can set various functions such aspower on/off, WDR mode on/off, zoom in/out, and on/off of the imagedisplay unit 28.

The sensor controller 42 may control a mechanical or electronic shutterincluded in the WDR image sensor 30. In addition, the sensor controller42 may be linked with a flash to control a flashing function. A lenscontroller 44 may control the focus or zoom magnification of thephotographing lens 20.

The system processor 40 may control overall operations of the imageprocessing apparatus 100. Programs executed by the system processor 40are recorded in a system memory 46 and executed as they are readsequentially. In addition, the system memory 46 may include an areawhich records system information and an area which records user settinginformation. Therefore, various information or settings can be read andrestored when the image processing apparatus 100 is operated. The systemmemory 46 may be implemented as a RAM, a flash memory, or an SSD.

A communication unit 48 has a communication function such as universalserial bus (USB), IEEE1394, local area network (LAN), etc. Thecommunication unit 48 may receive a control signal from a devicedifferent from the image processing apparatus 100 or transmit thegenerated WDR image to the device.

Each component described above with reference to FIGS. 2, 6 and 10 maybe implemented as a software component, such as a task, a class, asubroutine, a process, an object, an execution thread or a programperformed in a predetermined region of a memory, or a hardwarecomponent, such as a Field Programmable Gate Array (FPGA) or ApplicationSpecific Integrated Circuit (ASIC). In addition, the components may becomposed of a combination of the software and hardware components. Thecomponents may be reside on a computer-readable storage medium or may bedistributed over a plurality of computers.

And each block may represent a module, segment, or portion of code,which comprises one or more executable instructions for implementingspecified logical function(s). It should also be noted that in somealternative implementations, the functions noted in the blocks may occurout of the order. For example, two blocks shown in succession may infact be executed substantially concurrently or the blocks may sometimesbe executed in the reverse order, depending upon the functionalityinvolved.

FIG. 12 is a flowchart illustrating an image processing method performedby the image processing apparatus 100 according to an exemplaryembodiment.

Referring to FIG. 12, the image processing apparatus 100 sets the WDRimage sensor 30 and the ISP 70 to a 4WDR mode (operation S1). The WDRmode setting unit 60 analyses luminance of image data output from theWDR image sensor 30 (operation S2) and compares the luminance with afirst reference value and a second reference value smaller than thefirst reference value (operations S3 and S4). If the luminance isgreater than both the first and second reference values, the 4WDR modeis maintained (operation S1). If the luminance is between the firstreference value and the second reference value, operation S5 isperformed. If the luminance is smaller than the second reference value,operation S12 is performed.

In operation S5, the register setting unit 50 sets a maximum shutterspeed Vmax of the WDR image sensor 30 to twice a current maximum shutterspeed Fs (operation S5) and sets shutter speeds of four image channelsA, B, C and D to L, S, L and S, respectively (operation S6).

Here, the channel writer 72 of the ISP 70 records the four channels A,B, C and D in the input channel buffer 74 (operation S7), and thechannel reader 76 reads the first two A and B of the four channels A, B,C and D (operation S8). The WDR image generator 80 generates one WDRimage by synthesizing two sub-images included in the two channels A andB (operation S9). Similarly, the channel reader 78 reads the other two Cand D of the four channels A, B, C and D (operation S10). The WDR imagegenerator 80 generates another WDR image by synthesizing two sub-imagesincluded in the two channels C and D (operation S11). Then, operation S2is performed again.

In operation S12, the register setting unit 50 sets the maximum shutterspeed Vmax of the WDR image sensor 30 to four times the current maximumshutter time Fs (operation S12) and sets all of the shutter speeds ofthe fourth image channels A, B, C and D to L (operation S13).

Here, the channel writer 72 of the ISP 70 records the four channels A,B, C and D in the input channel buffer 74 (operation S14), and thechannel reader 76 reads the first channel A among the fourth channels A,B, C and D (operation S15). In this case, since only one sub-imageexists, the WDR synthesis process of the WDR image generator 80 isbypassed. Therefore, the single sub-image is output, as it is, as anormal image from the ISP 70 (operation S16). Then, the remainingchannels B, C and D are sequentially read one by one (operation S15),and normal images are output (operation S16). After the last one of thefour channels A, B, C and D is processed (Y in operation S17), operationS2 is performed again.

In the above exemplary embodiments, photographing mode switches amongthe 4WDR mode, the 2WDR mode, and the normal mode (non-WDR mode).However, the inventive concept is not limited to this example and alsoapplicable to a switch between WDR modes in which arbitrary numbers ofsub-images are synthesized. In addition, the inventive concept isapplicable to a mode change not only to a WDR mode in which a smallernumber of sub-images are synthesized but also to a WDR mode in which agreater number of sub-images are synthesized. For example, if the modechange process of FIG. 4 or FIG. 5 is performed in the reverse order, amode change to a WDR mode in which a greater number of sub-images aresynthesized can be fully accomplished.

In addition, in the normal mode, one sub-image is not synthesized. Inother words, the WDR synthesis process is bypassed. However, it shouldbe understood that the normal mode has been described as a process ofsynthesizing one sub-image for the sake of consistency in technicalexpression.

According to an image processing apparatus and method of the inventiveconcept, it is possible to minimize deterioration of image quality byadaptively varying a photographing mode according to an environment inwhich an image is captured.

In addition, it is possible to change modes between various WDR modes(including a normal mode) simply by changing a register value of animage sensor without the need to reset an ISP for each mode change.

Therefore, since there is no frame loss due to a delay in a mode changebetween various WDR modes, a natural output image can be obtained.

The operations or steps of the methods or algorithms described above canbe embodied as computer readable codes on a computer readable recordingmedium, or to be transmitted through a transmission medium. The computerreadable recording medium is any data storage device that can store datawhich can be thereafter read by a computer system. Examples of thecomputer readable recording medium include read-only memory (ROM),random-access memory (RAM), compact disc (CD)-ROM, digital versatiledisc (DVD), magnetic tape, floppy disk, and optical data storage device,not being limited thereto. The transmission medium can include carrierwaves transmitted through the Internet or various types of communicationchannel. The computer readable recording medium can also be distributedover network coupled computer systems so that the computer readable codeis stored and executed in a distributed fashion.

At least one of the components, elements, modules or units representedby a block as illustrated in FIGS. 2 and 6-10 may be embodied as variousnumbers of hardware, software and/or firmware structures that executerespective functions described above, according to an exemplaryembodiment. For example, at least one of these components, elements,modules or units may use a direct circuit structure, such as a memory, aprocessor, a logic circuit, a look-up table, etc. that may execute therespective functions through controls of one or more microprocessors orother control apparatuses. Also, at least one of these components,elements, modules or units may be specifically embodied by a module, aprogram, or a part of code, which contains one or more executableinstructions for performing specified logic functions, and executed byone or more microprocessors or other control apparatuses. Also, at leastone of these components, elements, modules or units may further includeor may be implemented by a processor such as a central processing unit(CPU) that performs the respective functions, a microprocessor, or thelike. Two or more of these components, elements, modules or units may becombined into one single component, element, module or unit whichperforms all operations or functions of the combined two or morecomponents, elements, modules or units. Also, at least part of functionsof at least one of these components, elements, modules or units may beperformed by another of these components, elements, modules or units.Further, although a bus is not illustrated in the above block diagrams,communication between the components, elements, modules or units may beperformed through the bus. Functional aspects of the above exemplaryembodiments may be implemented in algorithms that execute on one or moreprocessors. Furthermore, the components, elements, modules or unitsrepresented by a block or processing steps may employ any number ofrelated art techniques for electronics configuration, signal processingand/or control, data processing and the like.

In concluding the detailed description, those skilled in the art willappreciate that many variations and modifications can be made to thepreferred embodiments without substantially departing from theprinciples of the inventive concept. Therefore, the exemplaryembodiments disclosed herein are used in a generic and descriptive senseonly and not for purposes of limitation.

What is claimed is:
 1. An image processing apparatus comprising: animage sensor configured to output image data having a plurality of imagechannels; at least one processor configured to implement: a mode settingunit which changes a photographing mode from a first mode in which afirst number of sub-images are synthesized to a second mode in which asecond number of sub-images are synthesized, based on luminance of theoutput image data: and a register setting unit which changes a registervalue of the image sensor according to the second mode; and an imagesignal processor (ISP) configured to generate a result image bysynthesizing the second number of sub-images from the image dataaccording to the changed register value, wherein the second number ofsub-images have different exposure times, wherein the register valuecomprises a maximum shutter speed for each photographing mode and ashutter speed for each image channel, and wherein the maximum shutterspeed is set in inverse proportion to a number of sub-images to besynthesized for generating the result image.
 2. The apparatus of claim1, wherein the number of image channels output from the image sensor isconstant regardless of the photographing mode.
 3. The apparatus of claim1, wherein the ISP is configured to read the second number of imagechannels according to the second mode among the image channels includedin the image data output from the image sensor and generate the resultimage by synthesizing the second number of sub-images.
 4. The apparatusof claim 3, wherein the ISP is configured to implement: a channel writerwhich sequentially records in an input channel buffer the image channelsincluded in the image data output from the image sensor according to thesecond mode; a channel reader which reads the second number of imagechannels among the image channels recorded in the input channel bufferand records the second number of image channels in an output channelbuffer; and a wide dynamic range (WDR) image generator which synthesizessub-images corresponding to the second number of image channels recordedin the output channel buffer.
 5. The apparatus of claim 4, wherein theWDR image generator comprises: a sub-image generation unit configured togenerate the second number of sub-images respectively from the secondnumber of image channels recorded in the output channel buffer; and animage synthesis unit configured to generate the result image bysynthesizing the second number of sub-images.
 6. The apparatus of claim5, wherein the image synthesis unit is configured to generate the resultimage by assigning a different weight to each of the second number ofsub-images or to each area of each of the second number of sub-images.7. The apparatus of claim 1, wherein each of the first number ofsub-images and the second number of sub-images is an integer equal to orgreater than
 1. 8. The apparatus of claim 7, wherein each of the firstnumber of sub-images and the second number of sub-images is a power of2.
 9. The apparatus of claim 7, wherein the first number of sub-imagesis 4, and the second number of sub-images is 2 or
 1. 10. The apparatusof claim 1, wherein the mode setting unit determines the luminance ofthe output image data based on a mean of luminance of pixels included inthe output image data.
 11. The apparatus of claim 1, wherein the modesetting unit determines the luminance of the output image data based ona proportion of dark pixels whose luminance is equal to or lower than afirst predetermined level in the output image data or the proportion ofbright pixels whose luminance is equal to or higher than a secondpredetermined level in the output image data.
 12. A image processingmethod comprising: outputting image data having a plurality of imagechannels using an image sensor; changing a photographing mode from afirst mode in which a first number of sub-images are synthesized to asecond mode in which a second number of sub-images are synthesized,based on luminance of the output image data; changing a register valueof the image sensor according to the second mode; outputting modifiedimage data corresponding to the changed register value; and generating aresult image by synthesizing the second number of sub-images from themodified image data, wherein the second number of sub-images havedifferent exposure times, wherein the register value comprises a maximumshutter speed for each photographing mode and a shutter speed for eachimage channel, and wherein the maximum shutter speed is set in inverseproportion to a number of sub-images to be synthesized for generatingthe result image.
 13. The method of claim 12, wherein the number ofimage channels output from the image sensor is constant regardless ofthe photographing mode.
 14. The method of claim 12, wherein thegenerating of the result image comprises reading the second number ofimage channels according to the second mode among the image channelsincluded in the modified image data and generating the result image bysynthesizing the second number of sub-images.
 15. The method of claim12, wherein the generating of the image comprises: sequentiallyrecording the image channels included in the modified image data in aninput channel buffer; reading the second number of image channels amongthe image channels recorded in the input channel buffer; recording thesecond number of image channels in an output channel buffer; andsynthesizing sub-images corresponding to the second number of imagechannels recorded in the output channel buffer.
 16. The method of claim15, wherein the synthesizing of the second number of sub-imagescomprises: generating the second number of sub-images respectively fromthe second number of image channels recorded in the output channelbuffer; and generating the result image by synthesizing the secondnumber of sub-images.